Mycelium, the thread-like root network of fungi, is one of the most critical biological systems on Earth. It holds soil together, feeds forests, stores massive amounts of carbon, and is now being used to grow protein and clean up pollution. Plants allocated roughly 13.12 gigatons of CO2 equivalent to mycorrhizal fungal networks per year, equal to about 36% of annual fossil fuel emissions, making mycelium one of the planet’s largest living carbon sinks.
How Mycelium Holds Soil Together
Soil isn’t just dirt. It’s a structured system of tiny clumps called aggregates, and mycelium is a key reason those clumps hold their shape. The hyphae (microscopic fungal threads) physically weave through soil particles, binding them together. But the real trick is chemical: certain fungi, particularly arbuscular mycorrhizal fungi, produce a sticky glycoprotein called glomalin that acts as a biological glue.
Glomalin binds soil particles through what scientists describe as a “bonding, joining, packing” mechanism. Individual grains stick to fungal threads, then gradually form larger, more stable clumps. This matters because well-aggregated soil resists erosion, holds more water, retains heat better, and allows roots to penetrate more easily. Glomalin is also remarkably durable. It’s hydrophobic, difficult to break down, and persists in soil for long periods, which means it also helps lock away organic carbon underground.
The Underground Transport System
Mycelium doesn’t just sit in soil. It actively moves water, carbon, nitrogen, and phosphorus from one place to another, functioning like a microscopic pipeline network. Recent imaging work has revealed that fungal cords contain specialized hyphae with distinct roles. Some are large, hollow, and potentially dead, carrying water much like the vessels in a plant stem. Others are packed with internal membranes and organelles, shuttling carbon and nitrogen. The resemblance to a plant’s vascular system is striking.
Transport happens through a combination of active and passive mechanisms. Growth at hyphal tips creates pressure differences that pull cytoplasm (and dissolved nutrients) forward. Water also wicks along the outside of hyphae, carrying nutrients with it. Inside certain hyphae, tiny vacuoles store nutrients in dense granules rich in phosphorus, sulfur, and nitrogen, essentially acting as mobile storage containers that can release their cargo where it’s needed. Without water, this transport shuts down almost entirely, which is one reason drought is so damaging to soil ecosystems beyond its obvious effects on plants.
Forest Communication Networks
Trees in a forest are not isolated individuals. Most are connected underground through shared mycorrhizal networks, sometimes called “wood wide webs,” where fungal mycelium links the root systems of multiple plants. Through these networks, trees exchange carbon, water, nitrogen, phosphorus, and micronutrients. Carbon and nitrogen typically travel together as simple amino acids.
What makes this genuinely remarkable is that these networks also transmit chemical warnings. When tomato plants connected by mycorrhizal fungi were attacked by leaf-eating caterpillars, their healthy neighbors activated defense genes within six hours, before any pest reached them. The signaling appears to travel through pathways involving salicylic acid and jasmonic acid, the same stress-response chemicals plants use internally. The network essentially lets one plant’s immune alarm trigger a defensive response in its neighbors.
These connections aren’t always cooperative. Fungi also transport allelochemicals, compounds that suppress neighboring plants’ growth. Some species use the network to gain a competitive edge, sending growth-inhibiting chemicals to rivals. The network is less a utopian sharing system and more a complex web of cooperation, competition, and chemical communication that shapes which plants thrive in a given area.
A Massive Carbon Sink
An analysis of nearly 200 datasets produced the first global estimate of how much carbon flows from plants into mycorrhizal fungi. The numbers are enormous: plants channel roughly 13.12 gigatons of CO2 equivalent per year into fungal mycelium. Ectomycorrhizal fungi (the type that partners with most temperate forest trees) receive the lion’s share at 9.07 gigatons, while arbuscular mycorrhizal fungi (which partner with grasses, crops, and tropical trees) receive 3.93 gigatons.
This carbon is “at least temporarily” stored in the underground fungal network. Some of it gets metabolized and released, but a significant portion becomes part of persistent soil organic matter, especially through compounds like glomalin. The sheer scale of this flow, equivalent to more than a third of annual fossil fuel emissions, means that protecting and restoring fungal networks in soil isn’t just an ecological concern. It’s a climate one.
Cleaning Up Contaminated Land
Certain fungi can break down petroleum hydrocarbons and other pollutants that would otherwise persist in soil for decades. This process, called mycoremediation, uses the same enzymatic machinery fungi evolved to decompose wood and other tough organic materials. In trials using native fungal strains from the Ecuadorian Amazon, researchers achieved petroleum hydrocarbon removal rates above 95%, with one strain reaching 99.3%. For comparison, the same contaminated soil left to natural processes lost only about 12% of its hydrocarbons over the same period.
The fungi tested belonged to genera commonly found on dead wood (Ganoderma and Trametes), which produce powerful enzymes capable of dismantling complex organic molecules. This approach is particularly valuable in remote or ecologically sensitive areas where conventional cleanup methods like excavation or chemical treatment would cause additional damage.
Mycelium as Food
Mycelium is increasingly being grown as a protein source for human consumption. Fungi can produce protein ranging from 20% to 85% of their dry weight depending on species and growing conditions, competing favorably with soy, peas, chickpeas, and lupine. Some cultivated mycelium products contain around 41% protein by dry weight, which is higher than most commonly consumed plant proteins.
Beyond raw protein content, mycelium brings high dietary fiber and good digestibility. Its naturally fibrous texture makes it particularly well-suited as a base for meat alternatives, since the thread-like structure of hyphae mimics the grain of muscle tissue without extensive processing. The polysaccharide profile of mycelium differs from that of mushroom caps: while fruiting bodies tend to be rich in mannose-based sugars, mycelium contains more glucose-based polysaccharides. Both forms show similar immune-supporting properties in research, suggesting mycelium-based products can deliver comparable health benefits to whole mushrooms.
Why Losing Mycelium Matters
Intensive agriculture, soil compaction, fungicide use, and deforestation all damage mycelial networks. When these networks collapse, the consequences cascade. Soil loses its structure and erodes faster. Trees lose their nutrient-sharing partnerships and become more vulnerable to drought and disease. Carbon that would have been channeled underground stays in the atmosphere. Contaminated sites lose a natural cleanup crew.
Mycelium is not a single organism doing a single job. It is infrastructure: the connective tissue of terrestrial ecosystems, a nutrient distribution network, a carbon pipeline, a soil architect, and increasingly, a source of sustainable food and environmental cleanup. Its importance is difficult to overstate precisely because it operates out of sight, doing work that only becomes obvious when it stops.